Translation | Ribosome regulation by EF-G and EF-Tu

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The ribosome, the ribonucleoprotein particle responsible for protein synthesis, is a ribozyme, bearing the stamp of its origin in the RNA world. Although the individual reactions of protein synthesis are intrinsic catalytic properties of the ribosome, most are greatly accelerated or controlled by the action of extrinsic protein factors. During the elongation phase, two reactions, transfer RNA (tRNA) selection and translocation, are regulated by elongation factors Tu (EF-Tu) and G (EF-G), respectively. EF-Tu delivers aminoacyl-tRNA, in a ternary complex with guanosine triphosphate (GTP), to the ribosome. Binding of the correct aminoacyl-tRNA as dictated by messenger RNA (mRNA) initiates a sequence of events that includes a global conformational change in the 30S ribosomal subunit, the hydrolysis of GTP, a conformational change in EF-Tu, release of EF-Tu–GDP from the ribosome and accommodation of aminoacyl-tRNA into the ribosomal A site. Following peptide bond formation, EF-G binds to the ribosome and stimulates the concerted movement of tRNAs and mRNA by one codon, freeing the A site for the next round of tRNA selection. Although EF-Tu accelerates the forward rate constants for tRNA selection and allows the ribosome to use a proofreading mechanism to enhance discrimination, EF-G accelerates an otherwise slow reaction. These factors thereby contribute to the remarkable speed and accuracy of protein synthesis by the ribosome.

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Encyclopedia of Biological Chemistry: Third Edition